So-called "dry skin" is the first and the most obvious manifestation of a downward modification in the moisture content of the epidermis. It occurs more frequently during the cold season. But, it can be seen also in other periods of the year, for example following an extended and excessive exposure to solar rays (R. Jackson 27, 106 an B. A. Gilchrest, J. Soc. Cosmet. Chem. 32, 153).
According to published research, both the moisture content and the state of elasticity of the skin depend essentially upon the amount of water present at the level of the horny layer of the skin (stratum corneum). This is directly linked to a greater or lesser presence of Natural Moisturizing Factor (NMF). (J. Blank, J. Invest. Dermatol. 18 433-440 and K. Laden and R. Spitner, J. Soc. Cosmet. Chem. 18, 351).
NMF is a mixture of a series of amino-acids (containing about 12% of the sodium salt of 5-oxyproline) along with sugars.
The moisturizing activity effected by NMF would be basically due to this presence of the glutamic acid derivative, 5-oxyproline, which is currently better known as 2-pyrrolidone-carboxylic acid or by the abbreviation PCA (H. W. Speir and P. G. Pascher, Hautarzt, 7, 55, J. D. Middleton, Br. J. Dermat. 80, 437 and S. Tatsumi, Amer. Perf. 87,61).
PCA, transformed into glutamic acid by 5-oxyprolinase, takes part together with glyxine and cysteine in the metabolic cycles of glutathione (A. Meister "Metabolism and transport of glutathione and other glutamyl compounds" in "Functions of glutathione" A. Laron, S. Orrenius, A. Holmgren and B. Maunervik, Raven Press N.Y., page 1, 1983).
As is well known, glutathione is a tripeptide formed by elementary amino acids glycine, cysteine and glutamic acid. It is also known that, in the metabolic cycle, glutathione reaches the interior of the cells, rather than the intercellular tissue wherein the phenomena inherent to the moisturizing of the skin take place. It is consequently surprising that administering glycine associated with gelatin produces a highly favorable effect on the skin moisture, since, according to previous literature, the administration of glutamic acid, to which the presence of NMF is linked, could appear more promising to this end.
In the past, glycine (which is a known elementary amino acid) was used for the treatment of muscular dystrophy and it is known that an administration thereof orally has a favorable effect on the smooth mosculature.
Moreover, it is not known that an administration of gelatin alone could have a favorable influence on cutaneous moisturization.
Gelatin (which in the official pharmacopea is formally named "Gelatina F.U." or, according to the International name "Gelatinum"), is a known substance which is used, in particular, for the production of medicinal capsules.
In gelatin itself, among other things, a certain amount of glycine is present and it is a surprising fact that, while gelatin powder has no effect on the cutaneous moisture, the association thereof with additional glycine, in a determined proportion, makes it possible to obtain the desired effect upon cutaneous moisture.